Abstract: Forty-five male lambs (Gansu modern breeding sheep group) were divided into 9 treatments (5 animals in every treatment), killed and sampled at 0, 7, 14, 21, 28, 35, 42, 49 or 56 d respectively. The relative weight and pH value of contents in every compartment of forestomach, concentration and Molar proportion of volatile fatty acids, and activity of microbic enzymes of rumen contents were measured. The relative weight of contents (%total weight of content in stomach) in reticulorumen were linearly increase during 0 to 35 d(R²=0.93,P=0.00), and was 61.54% and 76.87% at 28 and 35 d respectively. There was lower pH value in contents of rumen, reticulum and omasum, it was changed between in 5.30 to 6.03, 5.37 to 6.42 and 5.39 to 6.15 respectively. It was mainly acetic acid fermentation type, and the ratio of acetic to propionic (A/P) was changed between 2.18 to 3.82 in rumen contents, and there was higher propionic concentration. The higher activity of protease, α-amylase, cellulase in rumen contents was respectively appeared at 21, 7 and 14 d. The functional development in forestome was preliminarily completed at 28 d in the conditions of this trial. With confined raising and supplying the suited supplementary diet from 7 d age in days, the early weaning technology may be used at 35 or 28 d after birth in lambs.